In the past, various types of station-platform safety monitoring devices have been proposed (refer to Japanese Unexamined Patent Application Publication No. 10-304346, Japanese Unexamined Patent Application Publication No. 2001-341642, Japanese Unexamined Patent Application Publication No. 2001-26266, Japanese Unexamined Patent Application Publication No. 2001-39303, Japanese Unexamined Patent Application Publication No. 10-341727, and so forth).
For example, as disclosed in Japanese Unexamined Patent Application Publication No. 10-304346, camera systems for monitoring the edge of a station platform, as shown in FIG. 2, are known. Such systems are installed at a nearly-horizontal angle so that a single camera can capture a long distance of about 40 meters in a lateral direction. Further, such systems are configured so that the images of several cameras are displayed in an image on a single screen, so as to be visually recognized by a person.
Therefore, an image-object area to be visually recognized is long (deep). Where many passengers come and go, passengers are hidden behind other passengers, which makes it difficult to see all the passengers. Further, since the cameras are installed at nearly horizontal angles, they are easily affected by the reflection of morning sunlight, evening sunlight, and other light, which often makes it difficult to pick up images properly.
Further, where a person falls onto a railroad track, a fall-detection mat shown in FIG. 3 detects the person fall by detecting the pressure thereof. However, since the fall-detection mat can be provided only on an inward part between the railroad track and the platform due to its structure. Therefore, where the person jumps over the detection mat when he fells, the detection mat is entirely useless.
For improving the above-described systems, Japanese Unexamined Patent Application Publication No. 13-341642 discloses a system in which a plurality of cameras is installed in a downward direction under the roof of a platform, so as to monitor an impediment.
The system calculates the difference between an image where no impediments are shown therein and a current image. Where any difference is output, the system determines that an impediment is detected. Further, Japanese Unexamined Patent Application Publication No. 10-311427 discloses a system configuration for detecting motion vectors of an object for the same purpose as that of the above-described system.
However, those systems often fail to detect impediments, especially for varying light and shadow. Therefore, those systems are not good enough to be used as monitoring systems.